LITMIR.BIZ

      FIG 24. The larvae of craneflies and other soil-dwelling invertebrates taken from garden lawns are important for Starlings and other species. (Jill Pakenham)

      It is also important to recognise the widespread use of insecticides and related compounds in gardens, since these have the potential to both reduce prey availability and to enter the food chain, where problems may then occur. More widely within the built environment there is the risk from pollution, such as with heavy metals (see Chapter 4), which can also impact on the availability of invertebrates and alter the composition of the prey communities available to foraging birds (Eeva et al., 2005).

      Fruits, seeds and nectar

      Garden plants can also provide food for visiting birds more directly, through their fruits and seeds; in fact, many plants rely on birds to act as dispersal agents for their seeds, offering a nutritious fleshy fruit to attract the bird to take the seed. For example, the natural foods taken by garden-wintering Blackcaps include the berries of Cotoneaster, Honeysuckle Lonicera, Holly Ilex aquifolium, Mistletoe Viscum album and Sea-buckthorn Hippophae rhamnoides. Blackcaps have also been reported feeding on the seeds of Daisy Bush Brachyglottis greyi (Hardy, 1978). The different fruits and seeds become available at different times of the year, though predominantly from October through to January, and this can alter the shape of the bird community visiting gardens. The movement into gardens of wintering Redwing, Fieldfare and Waxwing may reflect the availability of favoured berries in gardens and their scarcity elsewhere. It has been noted, for example, that the timing of hedgerow cutting within the UK’s arable landscapes may remove large quantities of the berry standing crop from the wider landscape, leaving gardens as an important resource (Croxton & Sparks, 2004).

      Some of these berries are favoured over others and in some cases a long fruiting season, such as in Holly, can suggest that the berry isn’t particularly favoured by visiting birds, only being eaten once other options are no longer available. In addition to the differences seen between different plant species, the nutritional characteristics of individual fruits may also vary with season. In many berries, the water content of the pulp decreases as the season progresses, while the average lipid content increases. Berry colour may be used as a signal, alerting berry-eating birds to the reward on offer, and there is evidence that birds may select fruits of a particular colour because of their nutritional value. Some bird species appear to select fruits with a high anthocyanin content; anthocyanin is an antioxidant and berries rich in this pigment tend to be black in colour or ultraviolet reflecting. Work on Blackcaps indicates that individuals actively select for anthocyanins in their diet and that they use fruit colour as an honest signal of anthocyanin rewards when foraging (Schaefer et al., 2007).

      The consequences of the variation seen in fruits leads to species-specific preferences within the bird species that feed upon them. A series of studies by David and Barbara Snow has highlighted some of these preferences. Mistle Thrush, for example, was found to favour sloes over haws, while the preference was reversed in both Redwing and Fieldfare. Song Thrush Turdus philomelos showed a clear preference for Yew Taxus baccata, Elder Sambucus nigra and Guelder Rose Viburnum opulus, and the apparent avoidance of rosehips, while Blackbird was found to be fairly catholic in its tastes (Snow & Snow, 1988). Blackcaps make use of smaller berries in gardens, such as those of Cotoneaster conspicua (Fitzpatrick, 1996a), reflecting their almost entirely frugivorous diet (when fruit is available) within the Mediterranean wintering area (Jordano & Herrera, 1981), although it is interesting to note the importance of supplementary foods presented at garden feeding stations highlighted by Plummer et al. (2015) and explored later in this chapter.